The present invention relates generally to telecommunications networks having private lines, and more particularly, to methods and apparatus for routing calls to one or more private lines terminated in a network.
Business customers often use private lines, also known as dedicated access lines, to serve the telecommunication needs of their large and typically distributed locations. FIG. 1 illustrates a conventional communications network 100, consisting of a plurality of switching nodes, such as the nodes 131-134, interconnected by a plurality of links or trunks, such as the links 141-146. In the public switched telephone network (PSTN), calls are generally routed based on a standard (public) numbering or dialing plan. For example, in the United States, a North American Numbering Plan (NANP) is used to route PSTN calls. The NANP scheme is a geographical numbering scheme with the format xe2x80x9cNPA-NXX-XXXX,xe2x80x9d where the NPA digits indicate a geographical area; the NXX digits indicate the local exchanges within a particular area and the last four digits identify a particular line or station served by the exchange. Each switch in a long distance network contains a translation table, which translates some or all of the NPA-NXX digits to determine the next route (trunk) in the path towards the destination switch. For PSTN calls, the long distance carrier hands-off the call to a terminating local exchange carrier (LEC), who completes the call to a station in a residential or business location.
Business customers frequently employ one or more high capacity private lines, which are directly connected between the customer location and the network of a long distance carrier without going through the network of the local exchange carrier. Business customers that employ a high capacity private line would like to originate and receive calls from the long distance carrier directly over the private line. For example, a calling party 110 desires to call a called party 120, connected by means of a private line 160. Since such private lines, however, are not part of the PSTN, it is unclear what telephone numbers should be assigned to each private line in order to complete incoming calls. The public NANP numbers discussed above are intended only for lines or stations served by the local exchange carrier network and the long distance carriers are not authorized to assign NANP numbers to provide special telecommunication services.
It has been suggested that long distance carriers identify private lines using NANP numbers that have been secured by the long distance carrier from local carriers. However, the scarce public numbering resources makes such reallocation of NANP numbers to private line customers impractical. In addition, such a solution requires each long distance carrier to have a contractual relationship with many local carriers in different regions of the country to serve their business customers. Finally, such a solution requires the entire ten-digit number to be processed in the long distance network, to select a particular private line.
As apparent from the above-described deficiencies with the use of public numbering plans for private lines, a method and apparatus that permit a plurality of numbering plans to be implemented in the same network. A further need exists for a private numbering plan for private line customers.
Generally, a method and apparatus are disclosed for implementing a plurality of numbering plans in a telecommunications network. A network in accordance with the present invention can support a novel private numbering plan for identifying private lines, as well as conventional public numbering plans, such as the NANP in the United States. In the illustrative embodiment of the invention, the hybrid numbering plan has a generic format of NPA-PPP-EXTN. The NPA value is a geographic component, in a similar manner to the NANP plan. The PPP value identifies private lines or trunks. The EXTN value carries the digits required by the called party, such as the private branch exchange (PBX) switch of a customer, through the network to the terminating private line. For example, the EXTN digits can correspond to the digits required by a customer PBX switch to route calls to stations connected to the PBX or to another PBX. The number of digits in each field of the illustrative hybrid numbering plan is for illustration only.
According to one aspect of the invention, a numbering plan flag differentiates each of the different numbering plans employed by a network, such as the private numbering plan and the public numbering plan, to establish a plurality of routing domains. If the numbering plan flag is set to a predefined value, each private line number can be identified as being part of the hybrid numbering plan. Thus, upon receipt of an incoming call, the entry switch determines whether the call is associated with a private or public numbering plan, and sets the numbering plan flag to an appropriate value, indicating whether a given number is a private plan number or a public number. Thereafter, the numbering plan flag value is carried with the call through the network as the call progresses from one switch to the next. Each node or switch uses the numbering plan flag to access the appropriate routing table and forward the call to the proper destination.
The present invention can be extended to create multiple domains, such as one or more domestic domains (NANP plan), one or more private domains (Private Numbering Plan), and one or more international domains (International Numbering Plan). The numbering plan flag can be configured to differentiate among each possible routing domain, for example, using multiple flags or multiple bits in a single flag.
Upon receipt of an incoming call, the entry switch determines whether the call is associated with a private or public numbering plan, for example, by accessing a local or centralized database. During digit analysis, the entry switch or centralized database maps the dialed digits into a network routing number. If the egress method provisioned in the database is by means of a private line, the switch/database sets the numbering plan flag value identifying the routing number as a private number. The numbering plan flag is forwarded with the call by each switch along the route. If the numbering plan flag indicates that the destination is a private line, the switch uses the xe2x80x9cprivatexe2x80x9d routing domain for digit translation. This process is repeated at all switches through which the call traverses. At the exit switch, the private portion of the routing number (NPA-PPP) is deleted and the remaining digits are sent over the private line to the customer location. At the final network node, the terminating switch can employ a delete/prefix function to delete the routing digits (NPA and PPP values), before forwarding the remaining digits (along with the prefix, if any) to the customer location.
Thus, in accordance with the present invention calls can be completed to private lines, without assigning public telephone numbers to the private lines. In addition, since the private numbering plan is under the control of the corresponding long distance carrier, the private numbering plan does not have to conform to any standard. The rules governing the format of the private numbers can be derived to meet the operational needs of the long distance carrier.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.